This invention relates to a combination lock mechanism, by which we mean a lock mechanism comprising an operating member which, when the mechanism is in use, normally imposes a constraint on an associated device but can undergo releasing movement to discontinue the constraint and a plurality of settable members, each of which can be set by an operator in a selected one of a number of alternative positions, it being necessary for the operator to establish a predetermined combination or one of two or more predetermined combinations of respective positions of the settable members before releasing movement of the operating member can occur. In some locks incorporating a combination lock mechanism, the settable members are accessible and are moved directly by the operator. In other locks incorporating a combination lock mechanism, the settable members are not accessible directly and a separate driving member is provided through which the operator transmits drive to the settable members.